Projection systems such as digital projectors or rear projection televisions include an image-forming device that projects a desired image. The image-forming device generates the desired image in response to light received from an image signal and a light source received through an illumination relay having a maximum numerical aperture.
The light source used in projection systems is often a multi-directional light source. A portion of the light generated by the multi-directional light source is directed toward the image-forming device and other portions of its generated light are directed in other directions. In some projection systems, an elliptical mirror is used to reflect most of light directed in other directions toward a spatial homogenizer, such as an integration rod, before it is directed to the image-forming device by the illumination relay. Attempts to increase efficiency of collection of the light have previously caused an increase in the maximum numerical aperture (i.e., the sine of angle of acceptance (or incidence)). This increase in the numerical aperture results in a greater angular spread of light exiting the spatial homogenizer. The illumination relay that transfers this light has an upper limit on its angle of acceptance and is unable to deal with the greater angular spread thus making this light having the greater angular spread essentially uncollectible. This uncollectible light may heat up the system and needlessly reduce contrast on the screen. Accordingly, a need exists for a more efficient light collection system.